bcachefs: factor out thread_with_file, thread_with_stdio

thread_with_stdio now knows how to handle input - fsck can now prompt to
fix errors.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

9 files changed, 459 insertions, 245 deletions

diff --git a/fs/bcachefs/Makefile b/fs/bcachefs/Makefile
index b81268418174..7423a3557c68 100644
--- a/fs/bcachefs/Makefile
+++ b/fs/bcachefs/Makefile
@@ -82,6 +82,7 @@ bcachefs-y		:=	\
 	super-io.o		\
 	sysfs.o			\
 	tests.o			\
+	thread_with_file.o	\
 	trace.o			\
 	two_state_shared_lock.o	\
 	util.o			\
diff --git a/fs/bcachefs/bcachefs.h b/fs/bcachefs/bcachefs.h
index 840f605eff1f..ffef6182a477 100644
--- a/fs/bcachefs/bcachefs.h
+++ b/fs/bcachefs/bcachefs.h
@@ -464,6 +464,7 @@ enum bch_time_stats {
 #include "replicas_types.h"
 #include "subvolume_types.h"
 #include "super_types.h"
+#include "thread_with_file_types.h"
 
 /* Number of nodes btree coalesce will try to coalesce at once */
 #define GC_MERGE_NODES		4U
@@ -478,12 +479,6 @@ enum bch_time_stats {
 
 struct btree;
 
-struct log_output {
-	spinlock_t		lock;
-	wait_queue_head_t	wait;
-	struct printbuf		buf;
-};
-
 enum gc_phase {
 	GC_PHASE_NOT_RUNNING,
 	GC_PHASE_START,
@@ -739,8 +734,8 @@ struct bch_fs {
 	struct super_block	*vfs_sb;
 	dev_t			dev;
 	char			name[40];
-	struct log_output	*output;
-	struct task_struct	*output_filter;
+	struct stdio_redirect	*stdio;
+	struct task_struct	*stdio_filter;
 
 	/* ro/rw, add/remove/resize devices: */
 	struct rw_semaphore	state_lock;
@@ -1252,6 +1247,15 @@ static inline bool bch2_dev_exists2(const struct bch_fs *c, unsigned dev)
 	return dev < c->sb.nr_devices && c->devs[dev];
 }
 
+static inline struct stdio_redirect *bch2_fs_stdio_redirect(struct bch_fs *c)
+{
+	struct stdio_redirect *stdio = c->stdio;
+
+	if (c->stdio_filter && c->stdio_filter != current)
+		stdio = NULL;
+	return stdio;
+}
+
 #define BKEY_PADDED_ONSTACK(key, pad)				\
 	struct { struct bkey_i key; __u64 key ## _pad[pad]; }
 
diff --git a/fs/bcachefs/chardev.c b/fs/bcachefs/chardev.c
index 22a52bc8406b..46db563e0497 100644
--- a/fs/bcachefs/chardev.c
+++ b/fs/bcachefs/chardev.c
@@ -11,16 +11,13 @@
 #include "replicas.h"
 #include "super.h"
 #include "super-io.h"
+#include "thread_with_file.h"
 
-#include <linux/anon_inodes.h>
 #include <linux/cdev.h>
 #include <linux/device.h>
-#include <linux/file.h>
 #include <linux/fs.h>
 #include <linux/ioctl.h>
-#include <linux/kthread.h>
 #include <linux/major.h>
-#include <linux/poll.h>
 #include <linux/sched/task.h>
 #include <linux/slab.h>
 #include <linux/uaccess.h>
@@ -31,65 +28,6 @@ static int copy_to_user_errcode(void __user *to, const void *from, unsigned long
 	return copy_to_user(to, from, n) ? -EFAULT : 0;
 }
 
-struct thread_with_file {
-	struct task_struct	*task;
-	int			ret;
-	bool			done;
-};
-
-static void thread_with_file_exit(struct thread_with_file *thr)
-{
-	if (thr->task) {
-		kthread_stop(thr->task);
-		put_task_struct(thr->task);
-	}
-}
-
-__printf(4, 0)
-static int run_thread_with_file(struct thread_with_file *thr,
-				const struct file_operations *fops,
-				int (*fn)(void *), const char *fmt, ...)
-{
-	va_list args;
-	struct file *file = NULL;
-	int ret, fd = -1;
-	struct printbuf name = PRINTBUF;
-	unsigned fd_flags = O_RDONLY|O_CLOEXEC|O_NONBLOCK;
-
-	va_start(args, fmt);
-	prt_vprintf(&name, fmt, args);
-	va_end(args);
-
-	thr->ret = 0;
-	thr->task = kthread_create(fn, thr, name.buf);
-	ret = PTR_ERR_OR_ZERO(thr->task);
-	if (ret)
-		goto err;
-
-	ret = get_unused_fd_flags(fd_flags);
-	if (ret < 0)
-		goto err_stop_task;
-	fd = ret;
-
-	file = anon_inode_getfile(name.buf, fops, thr, fd_flags);
-	ret = PTR_ERR_OR_ZERO(file);
-	if (ret)
-		goto err_put_fd;
-
-	fd_install(fd, file);
-	get_task_struct(thr->task);
-	wake_up_process(thr->task);
-	printbuf_exit(&name);
-	return fd;
-err_put_fd:
-	put_unused_fd(fd);
-err_stop_task:
-	kthread_stop(thr->task);
-err:
-	printbuf_exit(&name);
-	return ret;
-}
-
 /* returns with ref on ca->ref */
 static struct bch_dev *bch2_device_lookup(struct bch_fs *c, u64 dev,
 					  unsigned flags)
@@ -200,132 +138,33 @@ static long bch2_ioctl_incremental(struct bch_ioctl_incremental __user *user_arg
 #endif
 
 struct fsck_thread {
-	struct thread_with_file	thr;
-	struct printbuf		buf;
+	struct thread_with_stdio thr;
 	struct bch_fs		*c;
 	char			**devs;
 	size_t			nr_devs;
 	struct bch_opts		opts;
-
-	struct log_output	output;
-	DARRAY(char)		output2;
 };
 
-static void bch2_fsck_thread_free(struct fsck_thread *thr)
+static void bch2_fsck_thread_exit(struct thread_with_stdio *_thr)
 {
-	thread_with_file_exit(&thr->thr);
+	struct fsck_thread *thr = container_of(_thr, struct fsck_thread, thr);
 	if (thr->devs)
 		for (size_t i = 0; i < thr->nr_devs; i++)
 			kfree(thr->devs[i]);
-	darray_exit(&thr->output2);
-	printbuf_exit(&thr->output.buf);
 	kfree(thr->devs);
 	kfree(thr);
 }
 
-static int bch2_fsck_thread_release(struct inode *inode, struct file *file)
-{
-	struct fsck_thread *thr = container_of(file->private_data, struct fsck_thread, thr);
-
-	bch2_fsck_thread_free(thr);
-	return 0;
-}
-
-static bool fsck_thread_ready(struct fsck_thread *thr)
-{
-	return thr->output.buf.pos ||
-		thr->output2.nr ||
-		thr->thr.done;
-}
-
-static ssize_t bch2_fsck_thread_read(struct file *file, char __user *buf,
-				     size_t len, loff_t *ppos)
-{
-	struct fsck_thread *thr = container_of(file->private_data, struct fsck_thread, thr);
-	size_t copied = 0, b;
-	int ret = 0;
-
-	if ((file->f_flags & O_NONBLOCK) &&
-	    !fsck_thread_ready(thr))
-		return -EAGAIN;
-
-	ret = wait_event_interruptible(thr->output.wait,
-			fsck_thread_ready(thr));
-	if (ret)
-		return ret;
-
-	if (thr->thr.done)
-		return 0;
-
-	while (len) {
-		ret = darray_make_room(&thr->output2, thr->output.buf.pos);
-		if (ret)
-			break;
-
-		spin_lock_irq(&thr->output.lock);
-		b = min_t(size_t, darray_room(thr->output2), thr->output.buf.pos);
-
-		memcpy(&darray_top(thr->output2), thr->output.buf.buf, b);
-		memmove(thr->output.buf.buf,
-			thr->output.buf.buf + b,
-			thr->output.buf.pos - b);
-
-		thr->output2.nr += b;
-		thr->output.buf.pos -= b;
-		spin_unlock_irq(&thr->output.lock);
-
-		b = min(len, thr->output2.nr);
-		if (!b)
-			break;
-
-		b -= copy_to_user(buf, thr->output2.data, b);
-		if (!b) {
-			ret = -EFAULT;
-			break;
-		}
-
-		copied	+= b;
-		buf	+= b;
-		len	-= b;
-
-		memmove(thr->output2.data,
-			thr->output2.data + b,
-			thr->output2.nr - b);
-		thr->output2.nr -= b;
-	}
-
-	return copied ?: ret;
-}
-
-static __poll_t bch2_fsck_thread_poll(struct file *file, struct poll_table_struct *wait)
-{
-	struct fsck_thread *thr = container_of(file->private_data, struct fsck_thread, thr);
-
-	poll_wait(file, &thr->output.wait, wait);
-
-	return fsck_thread_ready(thr)
-		? EPOLLIN|EPOLLHUP
-		: 0;
-}
-
-static const struct file_operations fsck_thread_ops = {
-	.release	= bch2_fsck_thread_release,
-	.read		= bch2_fsck_thread_read,
-	.poll		= bch2_fsck_thread_poll,
-	.llseek		= no_llseek,
-};
-
 static int bch2_fsck_offline_thread_fn(void *arg)
 {
 	struct fsck_thread *thr = container_of(arg, struct fsck_thread, thr);
 	struct bch_fs *c = bch2_fs_open(thr->devs, thr->nr_devs, thr->opts);
 
-	thr->thr.ret = PTR_ERR_OR_ZERO(c);
-	if (!thr->thr.ret)
+	thr->thr.thr.ret = PTR_ERR_OR_ZERO(c);
+	if (!thr->thr.thr.ret)
 		bch2_fs_stop(c);
 
-	thr->thr.done = true;
-	wake_up(&thr->output.wait);
+	thread_with_stdio_done(&thr->thr);
 	return 0;
 }
 
@@ -354,11 +193,6 @@ static long bch2_ioctl_fsck_offline(struct bch_ioctl_fsck_offline __user *user_a
 
 	thr->opts = bch2_opts_empty();
 	thr->nr_devs = arg.nr_devs;
-	thr->output.buf	= PRINTBUF;
-	thr->output.buf.atomic++;
-	spin_lock_init(&thr->output.lock);
-	init_waitqueue_head(&thr->output.wait);
-	darray_init(&thr->output2);
 
 	if (copy_from_user(devs, &user_arg->devs[0],
 			   array_size(sizeof(user_arg->devs[0]), arg.nr_devs))) {
@@ -384,16 +218,15 @@ static long bch2_ioctl_fsck_offline(struct bch_ioctl_fsck_offline __user *user_a
 			goto err;
 	}
 
-	opt_set(thr->opts, log_output, (u64)(unsigned long)&thr->output);
+	opt_set(thr->opts, stdio, (u64)(unsigned long)&thr->thr.stdio);
 
-	ret = run_thread_with_file(&thr->thr,
-				   &fsck_thread_ops,
-				   bch2_fsck_offline_thread_fn,
-				   "bch-fsck");
+	ret = bch2_run_thread_with_stdio(&thr->thr,
+			bch2_fsck_thread_exit,
+			bch2_fsck_offline_thread_fn);
 err:
 	if (ret < 0) {
 		if (thr)
-			bch2_fsck_thread_free(thr);
+			bch2_fsck_thread_exit(&thr->thr);
 		pr_err("ret %s", bch2_err_str(ret));
 	}
 	kfree(devs);
@@ -592,7 +425,7 @@ static int bch2_data_job_release(struct inode *inode, struct file *file)
 {
 	struct bch_data_ctx *ctx = container_of(file->private_data, struct bch_data_ctx, thr);
 
-	thread_with_file_exit(&ctx->thr);
+	bch2_thread_with_file_exit(&ctx->thr);
 	kfree(ctx);
 	return 0;
 }
@@ -642,10 +475,9 @@ static long bch2_ioctl_data(struct bch_fs *c,
 	ctx->c = c;
 	ctx->arg = arg;
 
-	ret = run_thread_with_file(&ctx->thr,
-				   &bcachefs_data_ops,
-				   bch2_data_thread,
-				   "bch-data/%s", c->name);
+	ret = bch2_run_thread_with_file(&ctx->thr,
+			&bcachefs_data_ops,
+			bch2_data_thread);
 	if (ret < 0)
 		kfree(ctx);
 	return ret;
@@ -936,8 +768,8 @@ static int bch2_fsck_online_thread_fn(void *arg)
 	struct fsck_thread *thr = container_of(arg, struct fsck_thread, thr);
 	struct bch_fs *c = thr->c;
 
-	c->output_filter = current;
-	c->output = &thr->output;
+	c->stdio_filter = current;
+	c->stdio = &thr->thr.stdio;
 
 	/*
 	 * XXX: can we figure out a way to do this without mucking with c->opts?
@@ -949,11 +781,10 @@ static int bch2_fsck_online_thread_fn(void *arg)
 	c->curr_recovery_pass = BCH_RECOVERY_PASS_check_alloc_info;
 	bch2_run_online_recovery_passes(c);
 
-	c->output = NULL;
-	c->output_filter = NULL;
+	c->stdio = NULL;
+	c->stdio_filter = NULL;
 
-	thr->thr.done = true;
-	wake_up(&thr->output.wait);
+	thread_with_stdio_done(&thr->thr);
 
 	up(&c->online_fsck_mutex);
 	bch2_ro_ref_put(c);
@@ -988,11 +819,6 @@ static long bch2_ioctl_fsck_online(struct bch_fs *c,
 
 	thr->c = c;
 	thr->opts = bch2_opts_empty();
-	thr->output.buf	= PRINTBUF;
-	thr->output.buf.atomic++;
-	spin_lock_init(&thr->output.lock);
-	init_waitqueue_head(&thr->output.wait);
-	darray_init(&thr->output2);
 
 	if (arg.opts) {
 		char *optstr = strndup_user((char __user *)(unsigned long) arg.opts, 1 << 16);
@@ -1005,15 +831,14 @@ static long bch2_ioctl_fsck_online(struct bch_fs *c,
 			goto err;
 	}
 
-	ret = run_thread_with_file(&thr->thr,
-				   &fsck_thread_ops,
-				   bch2_fsck_online_thread_fn,
-				   "bch-fsck");
+	ret = bch2_run_thread_with_stdio(&thr->thr,
+			bch2_fsck_thread_exit,
+			bch2_fsck_online_thread_fn);
 err:
 	if (ret < 0) {
 		bch_err_fn(c, ret);
 		if (thr)
-			bch2_fsck_thread_free(thr);
+			bch2_fsck_thread_exit(&thr->thr);
 		up(&c->online_fsck_mutex);
 		bch2_ro_ref_put(c);
 	}
diff --git a/fs/bcachefs/error.c b/fs/bcachefs/error.c
index aa4f7f4925f6..8a8bcbcdff2a 100644
--- a/fs/bcachefs/error.c
+++ b/fs/bcachefs/error.c
@@ -2,6 +2,7 @@
 #include "bcachefs.h"
 #include "error.h"
 #include "super.h"
+#include "thread_with_file.h"
 
 #define FSCK_ERR_RATELIMIT_NR	10
 
@@ -69,40 +70,66 @@ enum ask_yn {
 	YN_ALLYES,
 };
 
+static enum ask_yn parse_yn_response(char *buf)
+{
+	buf = strim(buf);
+
+	if (strlen(buf) == 1)
+		switch (buf[0]) {
+		case 'n':
+			return YN_NO;
+		case 'y':
+			return YN_YES;
+		case 'N':
+			return YN_ALLNO;
+		case 'Y':
+			return YN_ALLYES;
+		}
+	return -1;
+}
+
 #ifdef __KERNEL__
-#define bch2_fsck_ask_yn()	YN_NO
+static enum ask_yn bch2_fsck_ask_yn(struct bch_fs *c)
+{
+	struct stdio_redirect *stdio = c->stdio;
+
+	if (c->stdio_filter && c->stdio_filter != current)
+		stdio = NULL;
+
+	if (!stdio)
+		return YN_NO;
+
+	char buf[100];
+	int ret;
+
+	do {
+		bch2_print(c, " (y,n, or Y,N for all errors of this type) ");
+
+		int r = bch2_stdio_redirect_readline(stdio, buf, sizeof(buf) - 1);
+		if (r < 0)
+			return YN_NO;
+		buf[r] = '\0';
+	} while ((ret = parse_yn_response(buf)) < 0);
+
+	return ret;
+}
 #else
 
 #include "tools-util.h"
 
-enum ask_yn bch2_fsck_ask_yn(void)
+static enum ask_yn bch2_fsck_ask_yn(struct bch_fs *c)
 {
 	char *buf = NULL;
 	size_t buflen = 0;
-	bool ret;
+	int ret;
 
-	while (true) {
+	do {
 		fputs(" (y,n, or Y,N for all errors of this type) ", stdout);
 		fflush(stdout);
 
 		if (getline(&buf, &buflen, stdin) < 0)
 			die("error reading from standard input");
-
-		strim(buf);
-		if (strlen(buf) != 1)
-			continue;
-
-		switch (buf[0]) {
-		case 'n':
-			return YN_NO;
-		case 'y':
-			return YN_YES;
-		case 'N':
-			return YN_ALLNO;
-		case 'Y':
-			return YN_ALLYES;
-		}
-	}
+	} while ((ret = parse_yn_response(buf)) < 0);
 
 	free(buf);
 	return ret;
@@ -221,10 +248,13 @@ int bch2_fsck_err(struct bch_fs *c,
 			int ask;
 
 			prt_str(out, ": fix?");
-			bch2_print_string_as_lines(KERN_ERR, out->buf);
+			if (bch2_fs_stdio_redirect(c))
+				bch2_print(c, "%s", out->buf);
+			else
+				bch2_print_string_as_lines(KERN_ERR, out->buf);
 			print = false;
 
-			ask = bch2_fsck_ask_yn();
+			ask = bch2_fsck_ask_yn(c);
 
 			if (ask >= YN_ALLNO && s)
 				s->fix = ask == YN_ALLNO
@@ -253,8 +283,12 @@ int bch2_fsck_err(struct bch_fs *c,
 	     !(flags & FSCK_CAN_IGNORE)))
 		ret = -BCH_ERR_fsck_errors_not_fixed;
 
-	if (print)
-		bch2_print_string_as_lines(KERN_ERR, out->buf);
+	if (print) {
+		if (bch2_fs_stdio_redirect(c))
+			bch2_print(c, "%s\n", out->buf);
+		else
+			bch2_print_string_as_lines(KERN_ERR, out->buf);
+	}
 
 	if (!test_bit(BCH_FS_fsck_done, &c->flags) &&
 	    (ret != -BCH_ERR_fsck_fix &&
diff --git a/fs/bcachefs/opts.h b/fs/bcachefs/opts.h
index 42cad83efb48..a6f5185ecd67 100644
--- a/fs/bcachefs/opts.h
+++ b/fs/bcachefs/opts.h
@@ -414,11 +414,11 @@ enum fsck_err_opts {
 	  OPT_BOOL(),							\
 	  BCH2_NO_SB_OPT,		false,				\
 	  NULL,		"Allocate the buckets_nouse bitmap")		\
-	x(log_output,			u64,				\
+	x(stdio,			u64,				\
 	  0,								\
 	  OPT_UINT(0, S64_MAX),						\
 	  BCH2_NO_SB_OPT,		false,				\
-	  NULL,		"Pointer to a struct log_output")		\
+	  NULL,		"Pointer to a struct stdio_redirect")		\
 	x(project,			u8,				\
 	  OPT_INODE,							\
 	  OPT_BOOL(),							\
diff --git a/fs/bcachefs/super.c b/fs/bcachefs/super.c
index 0f3a924ca1f9..64ff7da49860 100644
--- a/fs/bcachefs/super.c
+++ b/fs/bcachefs/super.c
@@ -88,14 +88,11 @@ const char * const bch2_fs_flag_strs[] = {
 
 void __bch2_print(struct bch_fs *c, const char *fmt, ...)
 {
-	struct log_output *output = c->output;
-	va_list args;
-
-	if (c->output_filter && c->output_filter != current)
-		output = NULL;
+	struct stdio_redirect *stdio = bch2_fs_stdio_redirect(c);
 
+	va_list args;
 	va_start(args, fmt);
-	if (likely(!output)) {
+	if (likely(!stdio)) {
 		vprintk(fmt, args);
 	} else {
 		unsigned long flags;
@@ -103,11 +100,11 @@ void __bch2_print(struct bch_fs *c, const char *fmt, ...)
 		if (fmt[0] == KERN_SOH[0])
 			fmt += 2;
 
-		spin_lock_irqsave(&output->lock, flags);
-		prt_vprintf(&output->buf, fmt, args);
-		spin_unlock_irqrestore(&output->lock, flags);
+		spin_lock_irqsave(&stdio->output_lock, flags);
+		prt_vprintf(&stdio->output_buf, fmt, args);
+		spin_unlock_irqrestore(&stdio->output_lock, flags);
 
-		wake_up(&output->wait);
+		wake_up(&stdio->output_wait);
 	}
 	va_end(args);
 }
@@ -724,7 +721,7 @@ static struct bch_fs *bch2_fs_alloc(struct bch_sb *sb, struct bch_opts opts)
 		goto out;
 	}
 
-	c->output = (void *)(unsigned long) opts.log_output;
+	c->stdio = (void *)(unsigned long) opts.stdio;
 
 	__module_get(THIS_MODULE);
 
diff --git a/fs/bcachefs/thread_with_file.c b/fs/bcachefs/thread_with_file.c
new file mode 100644
index 000000000000..b24baeabf998
--- /dev/null
+++ b/fs/bcachefs/thread_with_file.c
@@ -0,0 +1,296 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "bcachefs.h"
+#include "printbuf.h"
+#include "thread_with_file.h"
+
+#include <linux/anon_inodes.h>
+#include <linux/file.h>
+#include <linux/kthread.h>
+#include <linux/pagemap.h>
+#include <linux/poll.h>
+
+void bch2_thread_with_file_exit(struct thread_with_file *thr)
+{
+	if (thr->task) {
+		kthread_stop(thr->task);
+		put_task_struct(thr->task);
+	}
+}
+
+int bch2_run_thread_with_file(struct thread_with_file *thr,
+			      const struct file_operations *fops,
+			      int (*fn)(void *))
+{
+	struct file *file = NULL;
+	int ret, fd = -1;
+	unsigned fd_flags = O_CLOEXEC;
+
+	if (fops->read && fops->write)
+		fd_flags |= O_RDWR;
+	else if (fops->read)
+		fd_flags |= O_RDONLY;
+	else if (fops->write)
+		fd_flags |= O_WRONLY;
+
+	char name[TASK_COMM_LEN];
+	get_task_comm(name, current);
+
+	thr->ret = 0;
+	thr->task = kthread_create(fn, thr, "%s", name);
+	ret = PTR_ERR_OR_ZERO(thr->task);
+	if (ret)
+		return ret;
+
+	ret = get_unused_fd_flags(fd_flags);
+	if (ret < 0)
+		goto err;
+	fd = ret;
+
+	file = anon_inode_getfile(name, fops, thr, fd_flags);
+	ret = PTR_ERR_OR_ZERO(file);
+	if (ret)
+		goto err;
+
+	fd_install(fd, file);
+	get_task_struct(thr->task);
+	wake_up_process(thr->task);
+	return fd;
+err:
+	if (fd >= 0)
+		put_unused_fd(fd);
+	if (thr->task)
+		kthread_stop(thr->task);
+	return ret;
+}
+
+static inline bool thread_with_stdio_has_output(struct thread_with_stdio *thr)
+{
+	return thr->stdio.output_buf.pos ||
+		thr->output2.nr ||
+		thr->thr.done;
+}
+
+static ssize_t thread_with_stdio_read(struct file *file, char __user *buf,
+				      size_t len, loff_t *ppos)
+{
+	struct thread_with_stdio *thr =
+		container_of(file->private_data, struct thread_with_stdio, thr);
+	size_t copied = 0, b;
+	int ret = 0;
+
+	if ((file->f_flags & O_NONBLOCK) &&
+	    !thread_with_stdio_has_output(thr))
+		return -EAGAIN;
+
+	ret = wait_event_interruptible(thr->stdio.output_wait,
+		thread_with_stdio_has_output(thr));
+	if (ret)
+		return ret;
+
+	if (thr->thr.done)
+		return 0;
+
+	while (len) {
+		ret = darray_make_room(&thr->output2, thr->stdio.output_buf.pos);
+		if (ret)
+			break;
+
+		spin_lock_irq(&thr->stdio.output_lock);
+		b = min_t(size_t, darray_room(thr->output2), thr->stdio.output_buf.pos);
+
+		memcpy(&darray_top(thr->output2), thr->stdio.output_buf.buf, b);
+		memmove(thr->stdio.output_buf.buf,
+			thr->stdio.output_buf.buf + b,
+			thr->stdio.output_buf.pos - b);
+
+		thr->output2.nr += b;
+		thr->stdio.output_buf.pos -= b;
+		spin_unlock_irq(&thr->stdio.output_lock);
+
+		b = min(len, thr->output2.nr);
+		if (!b)
+			break;
+
+		b -= copy_to_user(buf, thr->output2.data, b);
+		if (!b) {
+			ret = -EFAULT;
+			break;
+		}
+
+		copied	+= b;
+		buf	+= b;
+		len	-= b;
+
+		memmove(thr->output2.data,
+			thr->output2.data + b,
+			thr->output2.nr - b);
+		thr->output2.nr -= b;
+	}
+
+	return copied ?: ret;
+}
+
+static int thread_with_stdio_release(struct inode *inode, struct file *file)
+{
+	struct thread_with_stdio *thr =
+		container_of(file->private_data, struct thread_with_stdio, thr);
+
+	bch2_thread_with_file_exit(&thr->thr);
+	printbuf_exit(&thr->stdio.input_buf);
+	printbuf_exit(&thr->stdio.output_buf);
+	darray_exit(&thr->output2);
+	thr->exit(thr);
+	return 0;
+}
+
+#define WRITE_BUFFER		4096
+
+static inline bool thread_with_stdio_has_input_space(struct thread_with_stdio *thr)
+{
+	return thr->stdio.input_buf.pos < WRITE_BUFFER || thr->thr.done;
+}
+
+static ssize_t thread_with_stdio_write(struct file *file, const char __user *ubuf,
+				       size_t len, loff_t *ppos)
+{
+	struct thread_with_stdio *thr =
+		container_of(file->private_data, struct thread_with_stdio, thr);
+	struct printbuf *buf = &thr->stdio.input_buf;
+	size_t copied = 0;
+	ssize_t ret = 0;
+
+	while (len) {
+		if (thr->thr.done) {
+			ret = -EPIPE;
+			break;
+		}
+
+		size_t b = len - fault_in_readable(ubuf, len);
+		if (!b) {
+			ret = -EFAULT;
+			break;
+		}
+
+		spin_lock(&thr->stdio.input_lock);
+		if (buf->pos < WRITE_BUFFER)
+			bch2_printbuf_make_room(buf, min(b, WRITE_BUFFER - buf->pos));
+		b = min(len, printbuf_remaining_size(buf));
+
+		if (b && !copy_from_user_nofault(&buf->buf[buf->pos], ubuf, b)) {
+			ubuf += b;
+			len -= b;
+			copied += b;
+			buf->pos += b;
+		}
+		spin_unlock(&thr->stdio.input_lock);
+
+		if (b) {
+			wake_up(&thr->stdio.input_wait);
+		} else {
+			if ((file->f_flags & O_NONBLOCK)) {
+				ret = -EAGAIN;
+				break;
+			}
+
+			ret = wait_event_interruptible(thr->stdio.input_wait,
+					thread_with_stdio_has_input_space(thr));
+			if (ret)
+				break;
+		}
+	}
+
+	return copied ?: ret;
+}
+
+static __poll_t thread_with_stdio_poll(struct file *file, struct poll_table_struct *wait)
+{
+	struct thread_with_stdio *thr =
+		container_of(file->private_data, struct thread_with_stdio, thr);
+
+	poll_wait(file, &thr->stdio.output_wait, wait);
+	poll_wait(file, &thr->stdio.input_wait, wait);
+
+	__poll_t mask = 0;
+
+	if (thread_with_stdio_has_output(thr))
+		mask |= EPOLLIN;
+	if (thread_with_stdio_has_input_space(thr))
+		mask |= EPOLLOUT;
+	if (thr->thr.done)
+		mask |= EPOLLHUP|EPOLLERR;
+	return mask;
+}
+
+static const struct file_operations thread_with_stdio_fops = {
+	.release	= thread_with_stdio_release,
+	.read		= thread_with_stdio_read,
+	.write		= thread_with_stdio_write,
+	.poll		= thread_with_stdio_poll,
+	.llseek		= no_llseek,
+};
+
+int bch2_run_thread_with_stdio(struct thread_with_stdio *thr,
+			       void (*exit)(struct thread_with_stdio *),
+			       int (*fn)(void *))
+{
+	thr->stdio.input_buf = PRINTBUF;
+	thr->stdio.input_buf.atomic++;
+	spin_lock_init(&thr->stdio.input_lock);
+	init_waitqueue_head(&thr->stdio.input_wait);
+
+	thr->stdio.output_buf = PRINTBUF;
+	thr->stdio.output_buf.atomic++;
+	spin_lock_init(&thr->stdio.output_lock);
+	init_waitqueue_head(&thr->stdio.output_wait);
+
+	darray_init(&thr->output2);
+	thr->exit = exit;
+
+	return bch2_run_thread_with_file(&thr->thr, &thread_with_stdio_fops, fn);
+}
+
+int bch2_stdio_redirect_read(struct stdio_redirect *stdio, char *buf, size_t len)
+{
+	wait_event(stdio->input_wait,
+		   stdio->input_buf.pos || stdio->done);
+
+	if (stdio->done)
+		return -1;
+
+	spin_lock(&stdio->input_lock);
+	int ret = min(len, stdio->input_buf.pos);
+	stdio->input_buf.pos -= ret;
+	memcpy(buf, stdio->input_buf.buf, ret);
+	memmove(stdio->input_buf.buf,
+		stdio->input_buf.buf + ret,
+		stdio->input_buf.pos);
+	spin_unlock(&stdio->input_lock);
+
+	wake_up(&stdio->input_wait);
+	return ret;
+}
+
+int bch2_stdio_redirect_readline(struct stdio_redirect *stdio, char *buf, size_t len)
+{
+	wait_event(stdio->input_wait,
+		   stdio->input_buf.pos || stdio->done);
+
+	if (stdio->done)
+		return -1;
+
+	spin_lock(&stdio->input_lock);
+	int ret = min(len, stdio->input_buf.pos);
+	char *n = memchr(stdio->input_buf.buf, '\n', ret);
+	if (n)
+		ret = min(ret, n + 1 - stdio->input_buf.buf);
+	stdio->input_buf.pos -= ret;
+	memcpy(buf, stdio->input_buf.buf, ret);
+	memmove(stdio->input_buf.buf,
+		stdio->input_buf.buf + ret,
+		stdio->input_buf.pos);
+	spin_unlock(&stdio->input_lock);
+
+	wake_up(&stdio->input_wait);
+	return ret;
+}
diff --git a/fs/bcachefs/thread_with_file.h b/fs/bcachefs/thread_with_file.h
new file mode 100644
index 000000000000..05879c5048c8
--- /dev/null
+++ b/fs/bcachefs/thread_with_file.h
@@ -0,0 +1,41 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_THREAD_WITH_FILE_H
+#define _BCACHEFS_THREAD_WITH_FILE_H
+
+#include "thread_with_file_types.h"
+
+struct task_struct;
+
+struct thread_with_file {
+	struct task_struct	*task;
+	int			ret;
+	bool			done;
+};
+
+void bch2_thread_with_file_exit(struct thread_with_file *);
+int bch2_run_thread_with_file(struct thread_with_file *,
+			      const struct file_operations *,
+			      int (*fn)(void *));
+
+struct thread_with_stdio {
+	struct thread_with_file	thr;
+	struct stdio_redirect	stdio;
+	DARRAY(char)		output2;
+	void			(*exit)(struct thread_with_stdio *);
+};
+
+static inline void thread_with_stdio_done(struct thread_with_stdio *thr)
+{
+	thr->thr.done = true;
+	thr->stdio.done = true;
+	wake_up(&thr->stdio.input_wait);
+	wake_up(&thr->stdio.output_wait);
+}
+
+int bch2_run_thread_with_stdio(struct thread_with_stdio *,
+			       void (*exit)(struct thread_with_stdio *),
+			       int (*fn)(void *));
+int bch2_stdio_redirect_read(struct stdio_redirect *, char *, size_t);
+int bch2_stdio_redirect_readline(struct stdio_redirect *, char *, size_t);
+
+#endif /* _BCACHEFS_THREAD_WITH_FILE_H */
diff --git a/fs/bcachefs/thread_with_file_types.h b/fs/bcachefs/thread_with_file_types.h
new file mode 100644
index 000000000000..90b5e645e98c
--- /dev/null
+++ b/fs/bcachefs/thread_with_file_types.h
@@ -0,0 +1,16 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHEFS_THREAD_WITH_FILE_TYPES_H
+#define _BCACHEFS_THREAD_WITH_FILE_TYPES_H
+
+struct stdio_redirect {
+	spinlock_t		output_lock;
+	wait_queue_head_t	output_wait;
+	struct printbuf		output_buf;
+
+	spinlock_t		input_lock;
+	wait_queue_head_t	input_wait;
+	struct printbuf		input_buf;
+	bool			done;
+};
+
+#endif /* _BCACHEFS_THREAD_WITH_FILE_TYPES_H */